I don't trust telecommunications networks, and don't have a cell phone. I do, however, have a landline. I am not foolish enough to think that my conversations are private, so to reinforce the reality I use a public telephone in my house. I purchased it refurbished on eBay, but did not include working electrics. I pulled the board out of a tiny line-powered handset, soldered a connector to interface with the keypad, and put it all back together.
If you like this sort of thing, watch this video from featuring Ladyada and Phillip Torrone.